Electrodeposition of aluminum



Patented Aug. 22,

PATENT OFFICE ELECTRODERO SITION OF ALUDHNUM Frank C. Mathers,Bloomington, Ind., and Robert D. Blue, Midland, Mich.

No Drawing. Application May 10, 1937, Serial No. 141,706

3 Claims.

The present invention relates to the electrolytic plating with aluminumof other metals. The term aluminum, as employed in this description andin the appended claims, includes aluminum and alloys whereof aluminum isthe major constituent.

It is among the objects of the invention to provide an improved methodfor electrodepositing aluminum on metal articles. A further object ofthe invention is to provide a bath wherefrom aluminum can beelectrodeposited at substantially room temperature. Another object ofthe invention is to provide a bath for the electrodeposition of aluminumwhich has a relatively high electrical conductivity, and in which highelectrode efficiencies are obtained.

In our process for the electroplating with aluminum of dissimilar metalssuch as iron, copper, zinc, and the like, We employ a bath composedessentially of the reaction product or benzene with an alkyl halide andan aluminum halide. Certain derivatives of benzene, such as theallryl-benzenes, halo-benzenes, and alkyl-halobenzenes, can besubstituted for, or employed in combination with, benzene in forming ourplating bath; and hydrogen halides may be substituted for alkyl-halidesin such procedure.

In plating aluminum upon a dissimilar metal article, we employ thearticle to be plated as the 0 cathode in our bath, and a mass ofaluminum is attached to or employed as the anode therein. Direct currentis passed through the electrolyte whereby aluminum is dissolved off theanode into the bath and plated out on the cathode article. A supernatantliquid layer of benzene or derivative thereof is maintained over thebath to protect the same from oxidation by air and hydrolysis by themoisture normally present therein. The plating operation is carried outat room temperature, although elevated temperatures may be employed, e.g., 50 C.

In the preparation of our novel plating bath we have successfullyemployed benzene, and toluene, xylene, cymene, ethylbenzene,chlorobenzene, and bromobenzene, poly-methyl-benzene, andpoly-ethyl-benzene, as reaction materials instead of, or in combinationwith, benzene. Other materials of a similar nature which can be used areisopropyl benzene, tertiary butyl benzene, normal amyl benzene and thechloro-, br0mo-, and

iodo-, derivatives thereof. Certain of the foregoing materials or their.equivalents do not produce a bath which is sufliciently fluid at roomtemperatures for good operating conditions, and in such cases weadmixwith the material sufli- 5 cient benzene to produce a finalreaction product whereof the viscosity is lower than that obtained byusing such materials alone. Among the alkyl halides which are entirelysatisfactory for use as reactants in the preparation of the bath areethyl bromide, ethyl chloride, methyl chloride, isopropyl chloride,isopropyl bromide, normalbutyl chloride, tertiary amyl bromide, and thelike. Hydrogen chloride or hydrogen bromide may be substituted for thealkyl halide in preparing the plating bath. The third ingredient we usein the preparation of the bath is aluminum chloride, aluminum bromide,aluminum iodide, or mixtures of the foregoing. The supernatant liquidmaintained above the bath may be benzene, or any of the equivalentstherefor above named for use as reactants in preparing the bath.

A preferable way of combining the ingredients which we employ in makingup our bath comprises dissolving or suspending an aluminum halg5 ide, inanhydrous condition, in the benzene or derivative thereof, and thenmixing this product with the alkyl or hydrogen halide, preferably at asubstantially uniform rate over a suitable period of time. If the alkylhalide employed is a gas, or if hydrogen chloride is used in preparingthe bath, then the aluminum halide may be suspended in the benzene andsuch gaseous reagent bubbled thereinto. All of the reagents should be insubstantially anhydrous condition prior to 5 being combined. When a bathis being used for the first time, a small quantity of finely dividedmetallic aluminum may be added thereto advantageously. During the use ofthe bath in electrodepositing aluminum, it is sometimes necessary to addsmall quantities of freshly prepared electrolyte because the anodeefficiency is higher than the cathode efficiency. The addition of smallamounts of any of the alkyl halides herein mentioned gives equally goodresults, although the repeated addition thereof increases the viscosityof the electrode. Small amounts of the various components of theelectrolyte may be present in the supernatant layer.

The following table sets forth certain specific This application is acontinuation in part of our prior co-pending application Serial Number756,830.

Other modes of applying the principle of our Alkyl halide or hydrogenhalide Benzene or equivalent Aluminum halide 0130-57 C;Hr(OHs):-30

As a specific example illustrating the practice of our invention, wehave prepared a bath consisting of 88 parts by weight of benzene, 5'7parts by weight of ethyl bromide, 20 parts by weight of aluminumbromide, and 20 parts by weight of aluminum chloride, the total volumeof the plating solution being cubic centimeters. This bath was operatedat a temperature of 20 C. with the aluminum anode and copper cathodespaced 6.45 centimeters apart. The anode surface was 38.7 squarecentimeters, the cathode surface 6.4 square centimeters, and the bathwas operated at a current density of 1.55 amperes per square decimeterof cathode surface. In such bath the cathode efliciency was found to be76.52 and the anode efliciency 105.22. This bath was operated from 8 to10 hours daily for three months with excellent results. The anode losseswere higher than the cathode gain, so that additions of ethyl bromidewere necessary to maintain the bath. Three cubic centimeters of ethylbromide added after each hours of use were sufficient.

Aluminum alloy coatings may likewise be produced on a cathode in thebaths herein set forth. The alloy is employed as the anode in theelectrolysis. It is to be understood that alternate use as anode ofaluminum and a dissimilar metal gives an equivalent result. We haveemployed the alloys of aluminum with zinc, with copper, and withcadmium, as the anode in baths hereinbefore described to producedesirable coatings upon copper cathodes. We have also employed an anodeof aluminum alternately with a silver anode, a tin anode, a nickelanode, and various other metals, to produce aluminum alloy coatingspossessing desirable characteristics.

invention may be employed instead of those explained, change being madeas regards the process or materials herein disclosed, provided the meansor ingredients stated by any of the following claims or their equivalentbe employed.

We therefore particularly point out and distinctly claim as ourinvention:

1. The method of electrodepositing aluminum upon dissimilar metals whichcomprises passing direct current between an aluminum anode and adissimilar metal cathode in an electrolyte composed of the reactionproduct of: a material selected from the group consisting of benzene,and the alkyl-, halo-, and alkyl-halo-, derivatives of benzene; a halideselected from the group consisting of the alkyl and hydrogen halides;and an aluminum halide; under a layer comprising a material selectedfrom the group consisting of benzene, the alkyl-, halo-, andalkyl-halo-, derivatives of benzene.

2. The method of electrodepositing aluminum upon dissimilar metals whichcomprises passing direct current between an aluminum anode and adissimilar metal cathode in an electrolyte composed of the reactionproduct of benzene, an alkyl halide, and an aluminum halide, under alayer comprising benzene.

3. The method of electrodepositing aluminum upon dissimilar metals whichcomprises passing direct current between an aluminum anode and adissimilar metal cathode in an electrolyte composed of the reactionproduct of: an alkyl-benzene, an alkyl halide, and an aluminum halide;under a layer comprising an alkyl-benzene.

FRANK C. MATHERS. ROBERT D. BLUE.

